U.S. patent application number 14/827265 was filed with the patent office on 2016-02-25 for electromechanical system with predictive back-emf protection.
The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Anker Bjorn-Josefsen, Kim N. Madsen, Lars Risbo.
Application Number | 20160057533 14/827265 |
Document ID | / |
Family ID | 55349463 |
Filed Date | 2016-02-25 |
United States Patent
Application |
20160057533 |
Kind Code |
A1 |
Risbo; Lars ; et
al. |
February 25, 2016 |
ELECTROMECHANICAL SYSTEM WITH PREDICTIVE BACK-EMF PROTECTION
Abstract
A predictive back-emf protection methodology for an
electromechanical system, including a signal processor that
processes a source signal to provide a modified source signal, a
driver that converts the modified source signal to a drive signal,
and an electromechanical transducer that generates, from the drive
signal, a transducer response, and a back-emf signal coupled back
to the driver output. A predictive back-emf generator (such as a
routine in the signal processor) is characterized by a back-emf
transfer function (linear parameterized model of the
electromechanical transducer) for transforming an input signal into
a transform back-emf representation of a back-emf signal predicted
by the back-emf transfer function as a response of the
electromechanical transducer to such input signal. The signal
processor processes the source signal based on the transform
back-emf representation to generate the modified source signal
input to the driver. An example application is limiting peaking
current in an audio system.
Inventors: |
Risbo; Lars; (Hvalsoe,
DK) ; Bjorn-Josefsen; Anker; (Hellerup, DK) ;
Madsen; Kim N.; (Skovlunde, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Family ID: |
55349463 |
Appl. No.: |
14/827265 |
Filed: |
August 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62037426 |
Aug 14, 2014 |
|
|
|
Current U.S.
Class: |
381/55 |
Current CPC
Class: |
H04R 3/00 20130101; H04R
29/001 20130101; H04R 2203/00 20130101; H04R 3/007 20130101 |
International
Class: |
H04R 3/00 20060101
H04R003/00 |
Claims
1. An electromechanical system that generates back-emf
(electro-motive force), comprising a signal source configured to
provide a source signal; a signal processor configured to process
the source signal to provide a modified source signal; a driver
having an input and an output, and configured to convert the
modified source signal received at the input to a drive signal at
the output; an electromechanical transducer coupled to receive the
drive signal, and generate: a corresponding transducer response,
and a corresponding back-emf signal coupled back to the driver
output; a predictive back-emf generator characterized by a back-emf
transfer function corresponding to a linear parameterized model of
the electromechanical transducer, and configured to transform an
input signal into an output transform back-emf representation of a
back-emf signal predicted by the back-emf transfer function as a
response of the electromechanical transducer to such input signal;
the signal processor further configured to process the source
signal by receiving from the predictive back-emf generator a
transform back-emf representation corresponding to the source
signal, and modifying the source signal based on the transform
back-emf representation to generate the modified source signal;
such that the driver converts the modified source signal to the
drive signal.
2. The system of claim 1, wherein the predictive back-emf generator
comprises a routine executed by the signal processor.
3. The system of claim 1, wherein the signal source is an audio
signal source; and the electromechanical transducer is an audio
speaker, where the transducer response is audio signals generated
by the audio speaker.
4. The system of claim 3, wherein the drive signal is a drive
current; the back-emf signal is a back-emf current; the signal
processor processes the source signal such that the superposition
of the resulting drive current and the resulting back-emf current
at the driver output signal output is less than a pre-defined
peaking current threshold.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Priority is claimed under 37 CFR 1.78 and 35 USC 119(e) to
U.S. Provisional Application 62/037,426 (Docket TI-75268PS), filed
14 Aug. 2014, which is incorporated by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] This Patent Disclosure relates generally to
electromechanical systems that generate back-emf, and more
particularly to providing protection from back-emf for such
systems.
[0004] 2. Related Art
[0005] A Speaker is an electromechanical system that is capable of
storing energy in reactive electrical components, as well as in
mechanical components like moving masses and compressed
springs.
[0006] The amplifier drives current to the speaker coil (and
passive electrical components in the speaker). Mechanical energy
stored in the speaker coil and other mechanical components is
transformed back into a current that travels back to the
amplifier.
[0007] The magnitude of the back-EMF current can be large compared
to driven current. As a result, the total current at the amplifier
output can trigger overcurrent protection in situations where only
the driven current would not.
[0008] One approach for protecting against back-emf current is to
overdesign the amplifier to handle worst case current. This
solution disadvantageous particularly because the worst case
current is sporadic and seldom (based on combinations of audio and
speaker).
[0009] While this Background information references audio speaker
systems, the Disclosure in this Patent Document is not limited to
such applications, but is more generally directed to predictive
back-emf protection for electromechanical systems.
BRIEF SUMMARY
[0010] This Brief Summary is provided as a general introduction to
the Disclosure provided by the Detailed Description and Drawings,
summarizing aspects and features of the Disclosure. It is not a
complete overview of the Disclosure, and should not be interpreted
as identifying key elements or features of, or otherwise
characterizing or delimiting the scope of, the disclosed
invention.
[0011] The Disclosure describes apparatus and methods for
predictive back-emf protection adaptable to electromechanical
systems, such as providing predictive back-emf protection for an
audio speaker system to limit peaking current.
[0012] According to aspects of the Disclosure, signal processor
processes a source signal to provide a modified source signal. A
driver converts the modified source signal to a drive signal,
converted by an electromechanical transducer into a transducer
response, including generating a resulting back-emf signal coupled
back to the driver output. A predictive back-emf generator (such as
a routine in the signal processor) is characterized by a back-emf
transfer function (linear parameterized model of the
electromechanical transducer) for transforming an input signal into
a transform back-emf representation of a back-emf signal predicted
by the back-emf transfer function as a response of the
electromechanical transducer to such input signal. The signal
processor processes the source signal based on the transform
back-emf representation to generate the modified source signal
input to the driver.
[0013] Other aspects and features of the invention claimed in this
Patent Document will be apparent to those skilled in the art from
the following Disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates an example functional embodiment of an
audio system with digital audio input, including DSP processing and
a voltage amplifier driving a speaker, such as can adapted to use
predictive back-emf protection according to this Disclosure.
[0015] FIG. 2 illustrates an example functional embodiment of
predictive back-emf processing according to this Disclosure.
DETAILED DESCRIPTION
[0016] This Description and the Drawings constitute a Disclosure
for predictive back-emf protection in an electromechanical system,
including example embodiments that illustrate various technical
features and advantages.
[0017] This Disclosure is in the context of an example application
of adapting predictive back-emf protection to an audio speaker
system.
[0018] In brief overview, a predictive back-emf protection
methodology is adaptable to electromechanical systems. A signal
processor processes a source signal to provide a modified source
signal. A driver converts the modified source signal to a drive
signal, converted by an electromechanical transducer into a
transducer response, including generating a resulting back-emf
signal coupled back to the driver output. A predictive back-emf
generator (such as a routine in the signal processor) is
characterized by a back-emf transfer function (linear parameterized
model of the electromechanical transducer) for transforming an
input signal into a transform back-emf representation of a back-emf
signal predicted by the back-emf transfer function as a response of
the electromechanical transducer to such input signal. The signal
processor processes the source signal based on the transform
back-emf representation to generate the modified source signal
input to the driver.
[0019] FIG. 1 illustrates an example functional embodiment of an
audio system with digital audio input, such as can adapted to use
predictive back-emf protection according to this Disclosure.
[0020] A digital audio source supplies digital audio to an audio
processor (DSP and DAC). The DAC audio output drives an audio
amplifier. The audio amplifier drives a speaker unit.
[0021] The audio system can be adapted to provide protection for
back-emf using predictive back-emf processing according to the
Disclosure. Predictive back-emf protection is based on a linear
parameterized description of the speaker (and the gain in DAC and
amplifier). For the example embodiment, a predictive back-emf
algorithm is executed by the DSP. DSP predictive back-emf
processing (predictive of back-emf) is used to modify the audio
stream processed in the DSP to limit amplifier current due to
back-emf peaking.
[0022] FIG. 2 illustrates an example functional embodiment of
predictive back-emf processing according to this Disclosure.
[0023] The BACK-EMF Model block contains a linear model of the
back-emf that predicts the back-emf based on past speaker voltage
input. The example audio system in FIG. 1 uses a voltage amplifier,
so that the example embodiment of predictive back-emf processing to
provide current limit protection is described in the voltage
domain. That is, the back-emf model output is a current, but is
expressed in terms of a corresponding voltage over the speaker
resistive component, and in particular, the current threshold for
the amplifier is expressed in terms of a voltage UMAX.
[0024] An example transfer function model that applies for the
lower part of the audio spectrum, including accounting for the
current flowing into a speaker, can be found in J. W. Marshall
Leach, Introduction to electroacoustics & Audio Amplifier
Design. Kendall/Hunt Publishing company 2003.
[0025] With this transfer function model, the current into the
speaker can be expressed in terms of voice coil resistance, and
back-EMF:
i = u ( 1 R E - ( Bl ) 2 R E 2 1 j .PI. M MS + R MT + 1 j .PI. C MS
) ##EQU00001##
where the variables corresponds to the following psychical
parameters: R.sub.E: voice coil resistance at DC; BI: force factor;
M.sub.MS: mechanical mass of driver diaphragm assembly; C.sub.MS:
mechanical compliance of driver suspension; R.sub.MT: Total
mechanical damping. R.sub.MT is given by
R MT = R MS + ( Bl ) 2 R E ##EQU00002##
[0026] Other speaker models can be used.
[0027] Adapting predictive back-emf protection allows amplifier
design for expected-average operation. Predictive back-emf
processing is then used to predict back-emf current peaking based
on audio input, and modify the audio stream to compensate for such
predicted back-emf current peaking.
[0028] The Disclosed predictive back-emf protection methodology is
adaptable to other electromechanical system, providing protection
from back-emf current peaking, such protecting batteries from
current peaking.
[0029] The Disclosure provided by this Description and the Figures
sets forth example embodiments and applications illustrating
aspects and features of the invention, and does not limit the scope
of the invention, which is defined by the claims. Known circuits,
functions and operations are not described in detail to avoid
obscuring the principles and features of the invention. These
example embodiments and applications can be used by ordinarily
skilled artisans as a basis for modifications, substitutions and
alternatives to construct other embodiments, including adaptations
for other applications.
* * * * *